An object of the present invention is to improve the performance of a metal-air battery. The metal-air battery includes an air electrode, an anode, and an electrolyte sandwiched between the air electrode and the anode. The air electrode includes a co-continuous body having a three dimensional network structure formed by an integrated plurality of nanostructures having branches. A magnesium alloy is used for the anode, and a weak acidic salt containing no chloride ion or a salt considered to have a buffering capacity is used for the electrolyte. Consequently, the present invention can efficiently utilize electrons and suppress passivation and self corrosion of the anode, thereby improving the performance of the metal-air battery.